[bug #6743] Distinct NSNumbers with the same value dealloc each other

From:

nobody

Subject:

[bug #6743] Distinct NSNumbers with the same value dealloc each other

Date:

Tue, 25 Nov 2003 16:52:15 -0500

User-agent:

Mozilla/4.74 [en] (X11; U; Linux 2.0.36 i686)

=================== BUG #6743: LATEST MODIFICATIONS ==================
http://savannah.gnu.org/bugs/?func=detailbug&bug_id=6743&group_id=99
Changes by: Alexander Malmberg <address@hidden>
Date: Tue 11/25/2003 at 22:52 (Europe/Stockholm)
------------------ Additional Follow-up Comments ----------------------------
[NSNumber +numberWithLong:] returns an autoreleased object, not an object you
own. You might want to read
http://www.stepwise.com/Articles/Technical/HoldMe.html .
=================== BUG #6743: FULL BUG SNAPSHOT ===================
Submitted by: moseshall Project: GNUstep
Submitted on: Tue 11/25/2003 at 04:06
Category: Base/Foundation Severity: 5 - Major
Bug Group: Bug Resolution: None
Assigned to: None Status: Open
Summary: Distinct NSNumbers with the same value dealloc each other
Original Submission: Distinct NSNumbers with the *same value* can dealloc each
other. The following code snippet crashes gnustep-base 1.7.3 possibly because
of NSNumber caching. If I don't call [n1 release] there is no crash. If this is
due to caching strategy, then it can make NSNumber very fragile when numbers
are expected to persist as long as retained.
#include <Foundation/Foundation.h>
int main (int argc, const char *argv[], const char *env[])
{
NSNumber* n1 = [NSNumber numberWithLong:1];
NSNumber* n2 = [NSNumber numberWithLong:1];
NSLog(@"%@(%d)n", n1, [n1 retainCount]);
NSLog(@"%@(%d)n", n2, [n2 retainCount]);
[n1 release]; //<--problem here
// The next line crashes. n2 has gone away!
NSLog(@"%@(%d)n", n2, [n2 retainCount]);
return 0;
}
Thanks for your attention.
Brian 'Moses' Hall
address@hidden
Follow-up Comments
*******************
-------------------------------------------------------
Date: Tue 11/25/2003 at 22:52 By: alexm
[NSNumber +numberWithLong:] returns an autoreleased object, not an object you
own. You might want to read
http://www.stepwise.com/Articles/Technical/HoldMe.html .
-------------------------------------------------------
Date: Tue 11/25/2003 at 22:38 By: moseshall
I confess I don't understand how the test program fails to own the numbers n1
and n2, because it allocated them. I think given "principle of least surprise"
I expect these entities to be independent of each other, just as if they were
created using malloc() or if they were some other NSObject subclass. Doing
otherwise breaks retain/release balance. I would suggest ignoring a request to
dealloc a cached NSNumber if the program must keep track of how many identical
NSNumbers it has created (essentially duplicating the cache).
(Insert newbie disclaimer here.)
I would be curious to know how Cocoa handles the test program.
-------------------------------------------------------
Date: Tue 11/25/2003 at 12:09 By: ayers
Yes, that would be very good.
-------------------------------------------------------
Date: Tue 11/25/2003 at 11:40 By: CaS
What I was thinking of was making the cached numbers members of some new
subclass where -dealloc had been overridden to raise an exception. So there
would be no runtime overhead on dealloc of a non-cached number.
-------------------------------------------------------
Date: Tue 11/25/2003 at 11:17 By: ayers
In principal I agree, but it depends on the cost. I'm not sure how much the
hit would be, but expect numbers to be created and destroyed often in GDL2
based applications. So if each dealloc resulted in a hash look up... well,
depending on the implementation, I guess we may need to test it.
-------------------------------------------------------
Date: Tue 11/25/2003 at 09:00 By: CaS
I think raising an exception upon an attempt to deallocate a cached NSNumber
would be a nice feature.
-------------------------------------------------------
Date: Tue 11/25/2003 at 07:24 By: CaS
There is a bug in the test program ... it releases an object it does not own,
so a crash does not seem unreasonable (in the general case releasing objects
you don't own is bound to cause crashes).
Is the report a suggestion that the library should be changed to crash
elsewhere, or to have code added to watch for this case and raise an exception
or something similar, or perhaps to simply ignore the extra release and keep on
going?
CC list is empty
No files currently attached
For detailed info, follow this link:
http://savannah.gnu.org/bugs/?func=detailbug&bug_id=6743&group_id=99
_______________________________________________
Message sent via/by Savannah
http://savannah.gnu.org/